The present invention relates to a method and a related apparatus for off-loading incoherent material from a container. The subject apparatus is usable, in particular, in the chemical and/or pharmaceutical industry and wherever containers housing in their interior incoherent material constituted by dusts, fine-grain granulates or similar products need to be off-loaded.
Such containers are emptied in correspondence with an off-loading station, wherefrom the material housed therein is transferred towards a collecting tank or a collector connected, for instance, to a machine that uses the incoherent material itself for subsequent work processes. The collecting tank is positioned at a given level, and thereon is provided a support structure able to allow the positioning of a container at another level, higher than the previous one, thereby allowing the emptying of the container itself by gravity.
To allow the material to flow out of the superior container into the inferior container, connecting means are provided between the two levels, constituted by a rigid cylindrical conduit positioned vertically, within which a tubular sack is coaxially inserted, such sack presenting its own extremities respectively connected to the discharge outlet of the container and to the loading outlet of the tank or hopper.
The container is emptied by the passage of the dust contained therein through the tubular sack, which must be connected in substantially hermetic manner to the container and to the hopper so as not to let the dust exit: in practice, the dispersion of the dusts into the environment needs to be contained as much as possible.
For the closure of the tubular sack, as for the closure of the container, fastening means are used, such as bands or sealing rings, combined with controllable shut-off means such as butterfly valves and the like.
In spite of the presence of such fastening and closure means, in currently used apparatuses, a first problem relates to the possibility that dusts may be dispersed into the environment. This possibility is particularly considerable, in that the materials handled by the apparatuses in question are extremely prone to dispersion into the atmosphere due to their structure (meaning the size of the granules that compose them) and to their low specific gravity, so that the closure organs and fastening means in use may be found insufficient.
The relevance of the problem described above is all the greater the more the dusts treated in the apparatus considered above are constituted by substances or chemical compounds which are not easily degradable in the environment and, in some case, potentially harmful.
For this reason it is necessary to use tubular sacks that differ from substance to substance and thoroughly to clean the connection when shifting from one substance to another.
A further problem existing in the apparatuses considered above consists of the possibility that the dusts, during their passage from the superior container to the inferior tank through the aforementioned tubular sack, which usually presents a relatively large length (for instance on the order of two meters), de-mix. The separation of the various components constituting the dusts can easily occur, when opening the aforementioned shut-off organs, when a sizeable mass of dusts rapidly falls along the aforementioned tubular sack.
Apparatuses are known wherein, to eliminate the above drawback, the aforesaid tubular sack, or at least a considerable portion thereof, is not surrounded by the aforementioned rigid cylindrical conduit, and its superior portion, before the shut-off organs positioned at the outlet of the superior container are opened, is closed between the jaws of a "pliers element" able to slide vertically in the two directions along the tubular sack itself When the shut-off organs are opened, the mass of dust that enters into the tubular sack does not travel in a sudden manner through the sizeable gap that separates the superior container from the inferior tank, but immediately stops in correspondence with the restriction induced in the tubular sack itself by the aforesaid pliers element; this pliers element then starts to translate downwards, sliding in contact with the tubular sack and progressively opening the ever-larger portion of the tubular sack overlying it. As a consequence thereof, the tubular sack is progressively filled by the dusts, until, when the pliers element has arrived in proximity to the inferior tank, the jaws of the pliers element itself are opened and the dusts can freely start to flow towards the inferior tank.
The solution just described, while effective, is relatively complex and gives rise to considerable bulkiness of the portion of apparatus between the superior container and the inferior tank.